1. Technical Field
This invention relates to a method of adjusting the temperature properties of piezoelectric devices and oscillation circuits, especially a method of adjusting the temperature properties of the SAW device and oscillation circuits where it is mounted.
2. Prior Art
Conventionally, the temperature properties (frequency variation properties against the temperature variation) of piezoelectric resonators are expressed, as shown in FIG. 9, in terms of a second-order function such as in the tuning fork resonator and the SAW resonator in some and a third-order function such as in the AT resonator in others.
In the frequency temperature property of an oscillation circuit using this piezoelectric resonator, the oscillation circuit temperature property and the resonator temperature property are adjusted so that the temperature properties become minimal in the usage temperature range (xe2x88x9240 to +85xc2x0 C.) centering on the normal usage temperature of 25xc2x0 C. Normally, in an oscillator which has a piezoelectric resonator with a second-order function temperature property, if it is adjusted so that the peak temperature of the oscillation circuit temperature property becomes located in the center of the usage temperature range, the temperature stability becomes minimum. In a conventional resonator with a second-order function temperature property, the adjustment width of the peak temperature is about 0xc2x0 C. to 40xc2x0 C. On the other hand, because the point of inflection temperature cannot be easily adjusted in an AT-cut resonator etc. which have a third-order function temperature property, the first-order coefficient term is generally adjusted so that the oscillation circuit temperature property in the usage temperature range comes to have the minimum width. In actuality, the electrode film thickness and width are adjusted in the former piezoelectric resonator with a second-order function temperature property, and electrode forming direction (X-axis direction) is adjusted so that the rotation is centered on its inflection point in the latter resonator with a third-order function temperature property.
If an oscillation circuit is configured using a resonator with a second-order function temperature property, as shown in FIG. 8, the temperature property of the oscillation circuit is different from temperature property of the resonator in general. The temperature property seems to rotate in the clockwise direction or counter-clockwise direction. This is because the first-order coefficient of the temperature property varies. Although this variation of the temperature property contains not only a variation in the first-order coefficient but also a variation in the higher-order coefficients, it can be represented by a variation in the first-order coefficient in general. If the oscillator frequency and the temperature properties are minimized, as stated above, the peak temperature of the second-order function temperature property is adjusted to the center of the usage temperature range in general. However, the adjustment range of the peak temperature of a resonator is not free, and the adjustable range is limited.
On the other hand, if an oscillation circuit is configured using a resonator with a third-order function temperature property, as shown in FIG. 7, the temperature property of the oscillation circuit is different from the temperature property of the resonator in general. In the same way as in the case of the second-order property, the temperature property seems to rotate in the clockwise direction or counter-clockwise direction. In the case of the third-order function temperature property, moving the point of inflection temperature is difficult. Therefore, if the oscillator frequency and the temperature properties are minimized, it is arranged so that the minimum temperature property in the usage temperature range is obtained by adjusting the first-order coefficient of the resonator in general.
If the usage temperature range of an oscillator is mis-distributed relative to the temperature property adjustment range of the resonator, especially if the peak temperature of the second-order function temperature property cannot be set to the center of the usage temperature range, or if the point of inflection temperature of the third-order function temperature property is off the center of the usage temperature range, it is difficult to adjust so that the temperature property comes to have the minimum temperature width in the usage temperature range. Also, the SAW resonator normally has a second-order function temperature property, and as a method of improving the temperature property of the oscillation circuit, there is only one method where the peak temperature is brought to the center of the usage temperature range.
This invention has an objective of providing a method of adjusting the temperature properties of piezoelectric devices and oscillation circuits which can make the temperature properties of oscillation circuits flatter in the usage temperature range by using the property in the lower temperature range than the point of inflection of resonators with third-order function temperature properties.
In order to achieve the objective, the method of adjusting the temperature property of the piezoelectric device of this invention was configured as follows. Namely, a method of adjusting the temperature properties of piezoelectric devices which have a third-order function temperature property and the point of inflection of the third-order function temperature property outside the normal usage temperature range, the local maximum point or local minimum point temperature located in the normal temperature range is regarded as the peak temperature of the apparent second-order function temperature property, and the peak temperature was adjusted to the optimum value in the normal temperature range by rotating the temperature property around the point of inflection located outside the normal temperature range by adjusting the first-order coefficient.
Also, a method of adjusting the temperature properties of piezoelectric devices made of an in-plane rotated ST-cut quartz plate which is obtained by rotating a quartz plate around the electrical axis (X axis) and further rotated in a plane around the Zxe2x80x2 axis, the local maximum point or local minimum point temperature of the temperature property can also be adjusted to the optimum value in the normal temperature range by adjusting the in-plane rotation angle.
Further, a method of adjusting the temperature properties of piezoelectric devices made of an ST-cut quartz plate which is obtained by rotating a quartz plate around the electrical axis (X axis) and further rotated in a plane around the Zxe2x80x2 axis, is characterized by the fact that an ST-cut quartz plate rotated in plane around the Zxe2x80x2 axis is regarded as a third-order function temperature property. Further, that an adjustment of the temperature property in the normal temperature range is performed by rotating the temperature property around the point of inflection located outside the normal temperature range through adjusting the in-plane rotation angle to adjust the local maximum point or local minimum point of the temperature property to the optimum value in the normal temperature range as the peak temperature of an apparent second-order function temperature property.
In the configuration, the ST-cut quartz plate rotated in a plane around the Zxe2x80x2 axis is at xcex8=113 to 135 degrees and xcexa8=43xc2x15 degrees in the Euler angle. Also, the normal temperature range is set to xe2x88x9240 to +80xc2x0 C.
The method of adjusting the temperature properties of oscillation circuits of this invention is a method of adjusting the temperature properties of oscillation circuits where embedded is a piezoelectric device which has a third-order function temperature property and an inflection point of the third-order function temperature property outside the normal usage temperature range. Further, it is characterized by the fact that while the temperature property of the piezoelectric device is measured, the temperature property of the oscillation circuit is also measured to obtain their difference, the resonator temperature property which gives the temperature property required to the oscillation circuit is predicted, the local maximum point or local minimum point temperature located in the normal temperature range of the piezoelectric device is regarded as the peak temperature of an apparent second-order function temperature property so as to give the predicted temperature property, and the temperature property is rotated around the point of inflection located outside the normal temperature range through adjusting the first-order coefficient to adjust the peak temperature to the optimum value in the normal temperature range.
Also, the method of adjusting the temperature properties of oscillation circuits of this invention is configured so that the oscillation circuit is configured with a lower temperature range than the point of inflection of the third-order function temperature property of a piezoelectric resonator made of an in-plane rotated ST-cut quartz plate which is obtained by rotating a quartz plate around the electrical axis (X axis) further rotated in plane around the Zxe2x80x2 axis, and that the local maximum point or local minimum point temperature is regarded as the apparent peak temperature of the second-order function temperature property to adjust the frequency property of the oscillation circuit.
Also, this invention is a method of adjusting the temperature properties of oscillation circuits where embedded is an in-plane rotated ST-cut quartz plate which is obtained by rotating a quartz plate around the electrical axis (X axis) and further rotated in a plane around the Zxe2x80x2 axis, and it may have a configuration where the temperature properties of the ST-cut quartz plate rotated in plane and the oscillation circuit where embedded is the ST-cut quartz plate rotated in a plane are obtained, and that the temperature property of the ST-cut quartz plate rotated in a plane is adjusted so that their difference is canceled. In this case, the usage temperature range of the oscillation circuit is xe2x88x9240 to +85xc2x0 C.